update: checkout action version to v6

Author: UnschooledGamer

.github/workflows/on-demand-preview-releases-PR.yml

@@ -34,7 +34,7 @@ jobs:
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           clean: false
           fetch-depth: 0